Verified Commit f16b7a2b authored by Tommaso Tocci's avatar Tommaso Tocci
Browse files

Avoid optimization for readdir/opendir 

In the glibc both readdir and closedir functions marks the @dirp parameter
with a non-null attribute.
If we use a compiler optimization level grater then 1,
the `dirp == nullptr` expression is evaluated to false
at compilation time and the relative if blocks is cutted out
of the final binary.

In order to avoid this bheaviour, we implement a functions and then set
that as weak alias of the real glibc function call.
parent e9cb2605

ifs/include/preload/intcp_functions.hpp

0 → 100644
+27 −0
Original line number Diff line number Diff line 
#ifndef IFS_INTCP_FUNCTIONS_HPP

#define IFS_INTCP_FUNCTIONS_HPP



#include <dirent.h>



extern "C" {



# define weak_alias(name, aliasname) \

  extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));



/**

 * In the glibc headers the following two functions (readdir & opendir)

 * marks the @dirp parameter with a non-null attribute.

 * If we try to implement them directly instead of the weak aliased function,

 * the compiler will assume  that the parameter is actually null and

 * will optimized expression like `(dirp == nullptr)`.

*/



struct dirent* intcp_readdir(DIR* dirp);

weak_alias(intcp_readdir, readdir)



int intcp_closedir(DIR* dirp);

weak_alias(intcp_closedir, closedir)



#endif // IFS_INTCP_FUNCTIONS_HPP



} // extern C

ifs/src/preload/CMakeLists.txt

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ set(PRELOAD_HEADERS 
    ../../include/global/chunk_calc_util.hpp

    ../../include/preload/preload_context.hpp

    ../../include/preload/adafs_functions.hpp

    ../../include/preload/intcp_functions.hpp

    ../../include/preload/margo_ipc.hpp

    ../../include/preload/open_file_map.hpp

    ../../include/preload/open_dir.hpp

ifs/src/preload/intcp_functions.cpp

+3 −6
Original line number Diff line number Diff line
@@ -6,8 +6,7 @@ 
#include <preload/preload.hpp>

#include <preload/passthrough.hpp>

#include <preload/adafs_functions.hpp>



#include <dirent.h>

#include <preload/intcp_functions.hpp>





using namespace std;
@@ -473,9 +472,8 @@ DIR* opendir(const char* path){ 
    return (reinterpret_cast<decltype(&opendir)>(libc_opendir))(path);

}



struct dirent* readdir(DIR* dirp){

struct dirent* intcp_readdir(DIR* dirp){

    init_passthrough_if_needed();

    #pragma GCC diagnostic ignored "-Wnonnull-compare"

    if(dirp == nullptr){

        errno = EINVAL;

        return nullptr;
@@ -487,9 +485,8 @@ struct dirent* readdir(DIR* dirp){ 
    return (reinterpret_cast<decltype(&readdir)>(libc_readdir))(dirp);

}



int closedir(DIR* dirp) {

int intcp_closedir(DIR* dirp) {

    init_passthrough_if_needed();

    #pragma GCC diagnostic ignored "-Wnonnull-compare"

    if(dirp == nullptr){

        errno = EINVAL;

        return -1;